The invention relates generally to pressure sensors, and more particularly to a differential pressure measuring system.
Differential pressure sensors are used to measure pressure differences between two pressure sensing elements. The invention of the present application uses two pressure-sensing elements. The pressure sensing elements provide outputs proportional to their respective measured pressures. The difference between the outputs represents the differences between the measured pressures. Circuitry combined with the pressure sensing elements corrects the slope and offset characteristics of the output curves to improve pressure-measuring accuracy. For example, U.S. Pat. No. 4,196,382 to Bryzek, U.S. Pat. No. 5,193,393 to Czarnocki and U.S. Pat. No. 5,471,884 to Czarnocki et al. each adjusts the pressure sensing element outputs prior to combining the outputs to produce the differential pressure measurement. However, these references fail to optimize the differential pressure measurements.
One important application for differential pressure sensors is in the automobile industry, where they are used to measure the pressure difference between the engine""s exhaust and intake manifolds. In such applications, the sensors are exposed to harsh contaminants. It is desirable to isolate the sensor from the surrounding contaminants while still accurately measuring pressure. U.S. Pat. No. 5,471,884 to Czarnocki et al. describes one attempt to provide a differential pressure sensor isolated from the surrounding media by confirming the media to the insensitive backside surfaces of the piezo-resistive pressure sensor die. However, the Czarnocki circuitry fails to function reliably when the sensitive topside surfaces contact contaminants, causing shunting between the lead-wires and circuits.
A general object of the present invention is to provide a stable differential pressure measurement system which will protect delicate sensor electronics from harsh surrounding media. Another objective is for the system to provide accurate differential pressure measurements. These goals are achieved by the present invention comprising a first sensor, preferably a micro-machined semiconductive capacitive sensor, including a first diaphragm exposed on one side and having a sealed partially evacuated chamber within the first sensor on the other side of the first diaphragm, the first sensor providing a first sensor signal proportional to the difference between a first pressure applied across the exposed side of the first diaphragm and a second pressure applied across the chamber side of the first diaphragm; a second micro-machined semiconductive capacitive sensor including a second diaphragm exposed on one side and having a second sealed partially evacuated chamber within the second sensor on the other side of the second diaphragm, the second sensor providing a second sensor signal proportional to the difference between a third pressure applied across the exposed side of the second diaphragm and a fourth pressure applied across the chamber side of the second diaphragm, and circuitry for combining the first and second sensor signals to produce a differential-pressure output signal.
The invention also includes the method for performing a differential pressure measurement comprising the steps of: transporting a first fluid through a first intake to exert a first force on a first mass of gel, the gel transferring the force to a first sensor, preferably a micro-machined semiconductive capacitive sensor; transporting a second fluid through a second intake to exert a second force on a second mass of gel, the gel transferring the force to a second micro-machined semiconductive capacitive sensor; producing, from the first and second capacitive sensors, first and second sensor signals proportional to the first and second forces exerted on the first and second capacitive sensors; and combining the first and second output signals to produce a differential-pressure output signal.
The invention can be used in an exhaust system for an engine comprising exhaust and intake manifolds; first and second nozzles; a first and second conduits connecting the first nozzle to the exhaust manifold and the second nozzle to the intake manifold; a first sensor, preferably a micro-machined semiconductive capacitive sensor, including a first diaphragm exposed on one side to the exhaust manifold and having a sealed partially evacuated chamber within the first sensor on the other side of the first diaphragm, the first sensor providing a first sensor signal proportional to the difference between a first pressure applied across the exposed side of the first diaphragm and a second pressure applied across the chamber side of the first diaphragm; a second micro-machined semiconductive capacitive sensor including a second diaphragm exposed on one side to the intake manifold and having a second sealed partially evacuated chamber within the second sensor on the other side of the second diaphragm, the second sensor providing a second sensor signal proportional to the difference between a third pressure applied across the exposed side of the second diaphragm and a fourth pressure applied across the chamber side of the second diaphragm; a circuitry for combining the first and second signals to produce a differential-produce output signal representing the differential pressure between the exhaust and intake manifolds.
These objects as well as other objects, features and advantages of the invention will become more apparent to those skilled in the art from the following description with reference to the accompanying drawings.